Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted air charge and improving peak power outputs. The use of a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, but with additional fuel economy benefits. However, when the compressor operates under low air flow and/or high pressure ratio conditions, the compressor is prone to surge. For example, when an operator tips-out of an accelerator pedal, an engine intake throttle closes, leading to reduced forward flow through the compressor, and a potential for surge. Surge may lead to noise, vibration, and harshness (NVH) issues such as undesirable noise from the engine intake system. In extreme cases, surge may result in compressor damage.
To address compressor surge, engine systems may include a compressor recirculation valve (CRV) coupled across the compressor to recirculate compressed air from the compressor outlet to the compressor inlet allowing a decrease in pressure at the compressor outlet. As such, the CRV may degrade with use over time. For example, the CRV may be stuck at a given position and may not move when commanded. If the CRV is stuck open, it would constantly bleed off boosted air. As a result torque delivery and drivability may be reduced. If the CRV is stuck closed, compressor may surge more frequently resulting in increased NVH issues, and in severe cases, the compressor may be damaged.
In one example, some of the above issues may be at least partly addressed by a method for an engine, comprising: indicating degradation of a compressor recirculation valve based on a surge line adaptation of a surge line on a compressor map stored in a controller of the engine. By monitoring the adaptation of the surge line, degradation of the CRV may be detected.
As an example, the surge line may be learnt in real-time during one or more drive cycles by utilizing an adaptation algorithm. Specifically, the adaptation algorithm may advance the surge line when no surge is detected during aggressive tip-out conditions, and may retard the surge line when a threshold number of surge events are exceeded. As such, compressor surge may be determined based on a signal from a throttle inlet position sensor located downstream of the compressor. For example, during surge conditions, a frequency of the throttle inlet pressure sensor signal may be greater than a threshold.
If the CRV is stuck open, compressor flow may be greater than nominal. Consequently, compressor surge may be less likely to occur. In response to not detecting surge (during aggressive tip-outs, for example), the adaptation algorithm may continuously advance the surge line. That is, the algorithm may adjust the surge line to the left. When the surge line is advanced beyond an advance limit, it may be determined that the CRV is more open than desired.
If the CRV throttle is stuck closed, compressor surge events may increase. In response to increased compressor surge events, the adaptation algorithm may continuously retard the surge line. When the surge line is retarded beyond a retard limit, it may be determined that the CRV is more closed than desired.
In this way, by monitoring the adapted surge line, an engine control system may identify faults in the CRV when the adapted surge line is located beyond an expected range of surge lines. By detecting CRV throttle faults, and taking necessary remedial action, NVH issues may be reduced. Further, torque delivery and drivability may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.